The interrogation and multiplexing of long period grating curvature sensors using a Bragg grating based, derivative spectroscopy technique

Abstract

A long period grating is interrogated with a fibre Bragg grating using a derivative spectroscopy technique. A quasi-linear relationship between the output of the sensing scheme and the curvature experienced by the long period grating is demonstrated, with a sensitivity of 5.05 m and with an average curvature resolution of 2.9 × 10 −2 m −1 . In addition, the feasibility of multiplexing an in-line series of long period gratings with this interrogation scheme is demonstrated with two pairs of fibre Bragg gratings and long period gratings. With this arrangement the cross-talk error between channels was less than ±2.4 × 10 −3 m −1 .

Research Activities Arising From the University of Kent

“…I have a long interest in grating interrogation and multiplexing systems, developed originally at Kent, and have explored the use of arrayed waveguide gratings for interrogating both FBGs and interferometers [52,53], used an acousto-optic tuneable filter to provide high bandwidth interrogation of wavelength multiplexed FBGs [54] as well as developing a compact interferometer for grating interrogation using a highly birefringent fiber [55]. The work on LPGs has been applied to respiratory monitoring [56] where a multiplexing topology for the LPGs was interrogated using a variant of derivative spectroscopy [57].…”

Embedded progressive-three-layered fiber long-period gratings for respiratory monitoring

“…The sensing scheme that is being investigated is based upon a derivative spectroscopy technique in which an in-line series of sensing LPGs are being interrogated by spectrally matched fiber Bragg gratings. 27 For the intended application, a number of alternative ͑non-optical͒ sensing elements could also in principle be used. Most schemes are based on strain measurement ͑e.g., capacitance 28 and resistance 29 gauges or bistable switches 30 ͒ and as such are not directly applicable to surface profile reconstruction because a dynamic model of the motion of the thorax and abdomen during breathing would be required on which localized strain measurement could be used to infer changes in geometry.…”

“…27 Our approach allows the simple multiplexing of the sensors, providing the ability to scale up the approach to multiple sensors without a dramatic increase in the size of the peripheral electronics.…”

Application of long-period-grating sensors to respiratory plethysmography

“…Second, the curvature sensors are adhered to a garment to enable them to be used to detect the shape variations of the chest and abdominal regions of a human torso during respiration using the transmission spectrum of the LPGs' attenuation bands. Third, a curvature sensor array is used in conjunction with a signal-processing scheme based on derivative spectroscopy 11 to show the multiplexing capability of the interrogation scheme and to demonstrate the monitoring of a human subject during respiration. Fourth, analysis is performed on the acquired data to show that data from only six fully functional sensors is required to obtain approximately 6% volumetric error for the human subject used.…”